1. Field of the Invention
The present invention relates generally to a developing device used for developing an electrostatic latent image formed on an electrostatic latent image support member in an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly, to a developing device so adapted that a developer is contained in a developer containing portion, the developer thus contained is fed into a developer supplying member by a conveying member provided in the developer containing portion, and the developer is conveyed to the electrostatic latent image support member by the developer supplying member to supply the developer to the electrostatic latent image support member from the developer supplying member.
2. Description of the Prior Art
Examples of a developing device for developing an electrostatic latent image formed on an electrostatic latent image support member conventionally used in an image forming apparatus such as an electrophotographic copying machine or a printer includes one so adapted that a developer is contained in a developer containing portion, the developer thus contained is supplied to a developer supplying member by a conveying member provided in the developer containing portion, and the developer is conveyed to an electrostatic latent image support member by the developer supplying member to supply the developer to the electrostatic latent image support member from the developer supplying member as described above.
In such a developing device, a controlling member is generally brought into contact with the surface of the developer supplying member supplied with the developer by the conveying member as described above by applying pressure to charge the developer supplied to the surface of the developer supplying member by triboelectric charging as well as to control the amount of the developer on the surface of the developer supplying member so as to charge the developer conveyed to the electrostatic latent image support member by the developer supplying member.
Toner particles having a suitable average particle diameter are generally used as a developer used in such a developing device. However, the particle diameters of all the toner particles are not the same. More specifically, toner particles having various particle diameters exist, that is, the toner particles having particle diameters smaller than to larger than the average particle diameter exist to have a predetermined distribution.
When the controlling member is brought into contact with the surface of the developer supplying member supplied with the developer by applying pressure as described above to charge the developer by triboelectric charging as well as to control the amount of the developer on the surface of the developer supplying member, therefore, the toner particles having larger particle diameters in the developer supplied to the surface of the developer supplying member are removed from the surface of the developer supplying member by the controlling member, so that the toner particles having smaller particle diameters in the developer are first used for the development.
Furthermore, when the controlling member is brought into contact with the surface of the developer supplying member supplied with the developer by applying pressure as described above, such a phenomenon also occurs that the developer supplied to the surface of the developer supplying member is reduced to fine powder and a post-treating agent is embedded into the developer to deteriorate the developer due to the contact of the controlling member by applying pressure.
As a result, as the development proceeds using the above described developing device, the toner particles having larger particle diameters in the developer remain, and the amount of the developer deteriorated due to the contact of the controlling member by applying pressure is also increased.
Therefore, when an image is formed using the above described developing device, the image formed is not fogged and the developer is not spilled from the developing device in the initial stages in which the toner particles having smaller particle diameters in the developer contained in the developer containing portion are consumed, thereby to make it possible to achieve good image formation. As the development proceeds, however, the toner particles having larger particle diameters in the developer and the developer deteriorated are supplied to the developer supplying member and used for the development, so that the developer is not properly charged, for example, to introduce some problems. For example, the image formed is fogged so that the quality of the image is lowered, and the developer is spilled from the developer supplying member or scattered so that the inside of the image forming apparatus is made dirty by the developer.